The surface properties of a substance, such as surface potential, total amount of electric charge on the surface, surface charge density, electric field intensity on the surface and specific surface area, etc., not only are widely used in science researches in the fields of colloid and interface chemistry, material science, life science, soil science, ecological and environmental science and the like, but also are widely used in chemical engineering fields such as papermaking, cement, ceramics, chemical mechanical polishing, coal slurry, coating, cosmetics, food industry, mixing and dispersion system. Thus, determination on the surface property parameters of a substance appears particularly important.
Currently, for determining the total amount of electric charge on the surface, ion adsorption indicator and potentiometric titration method are commonly used. When using ion adsorption, one first needs to know the amount contributed to electrostatic adsorption from the total adsorption amount at H+ or OH−. However, the adsorption amount of involved in electrostatic adsorption cannot be predicted, due to H+ and OH− also involve adsorption of chemical bond. Thus, this method cannot determine the total amount of surface electric charge of a system containing variable charge under any pH value, any electrolyte concentration and any temperature. Further, the potentiometric titration method not only is not suitable for determining the total charge amount of a system containing permanent charge, but also is always questioned on its reliability, even for a variable charge system. Thus, so far there is no common method suited for determining total amount of substance surface charge in different conditions and different systems.
Currently, one method for determining a surface charge density of a substance is based on the following formula:
            σ      0        =                  T        C            S        ,
Wherein, σ0 is surface charge density, Tc is total amount of surface charge, and S is specific surface area.
Since the parameter of total amount of surface charge is required, the problem with determination of total amount of surface charge must also exist in the determination of surface charge density. Further, in the above formula, the specific surface area is also required. However, the result of the specific surface area may greatly vary, if different methods may be used to determine the specific surface area. Thus, for a method that determines surface charge density based on the parameter of specific surface area, the reliability of its result is hard to expect.
Conventionally, a second method for determining surface charge density is: upon obtaining the surface potential of the substance, correlation formula of Gouy-Chapman is used to indirectly obtain the surface charge density. However, up until now no widely applied method is available to accurately determine the surface potential. Thus, there are still difficulties to apply such method to determine surface charge density.
Currently, electric field intensity can be determined based on the below formula:
            E      0        =                            4          ⁢          π                ɛ            ⁢              σ        0              ,
Wherein, E0 is the surface electric field intensity, ∈ is the media dielectric constant, e.g., water has ∈=8.9×10−10 C2/Jdm. Due to depending on the surface charge density, same problem in determining surface charge density exists in determining surface electric field intensity.
In the prior art, there are a number of method for determining a substance specific surface area, such as commonly used inert gas adsorption method, ion negative adsorption method, glycol ethylene ether adsorption method, or glycerin adsorption method, etc. However, the results vary substantially by using these different methods for same substance.
In the present invention, substance surface potential is defined as the potential on the original surface of diffusion layer or OHP (outer Helmholtz surface) in the double electric layer. In the prior art, the method for determining substance surface potential includes: charge density method, negative adsorption method, positive adsorption method, dual-stage resonance (generation) method, pH indicator molecule method, fluorescence method, atomic force microscope method and Zeta potential method, and the like. All these methods have their own limitations. The charge density method, negative adsorption method, positive adsorption method and dual-stage resonance method are only suitable for determining surface potential of a constant charge sample of a single electrolyte system under neutral condition. The pH indicator molecule method, fluorescence method and atomic force microscope method may damage the condition of the substance surface per se, and thus the reliability of the result is difficult to say. Zeta potential method does not measure the surface potential. Rather, it measures the potential on the shear plane (or sliding surface) during electrophoresis, and the shear plane is often remote from the defined surface. The Zeta potential can be measured under different pH, electrolytes and temperature conditions. Since there is no method that can be widely used and accurately determine the surface potential under various conditions, Zeta potential has to be used as a substitute for surface potential. However, numerous studies over the years have shown that using Zeta potential to determine surface potential often is qualitative. In addition, Zeta potential method demands a very severe condition on the object to be tested, i.e., it requires that the particulate density of colloid suspension cannot be too high, while the size of particulate cannot be too large. Even for the new Zeta potentiometer (model Zetaprobe) by Colloidal Dynamics Inc., USA, the highest particulate density is only 60% (volume density). Thus, it is impossible to obtain a system with higher density, or “original state” measurement of solid particulate material.
Currently, Li Hang, et al. proposes a new method, i.e., with ion exchange equilibrium experiment and electrode method to realize combined measurement of five parameters including surface potential, specific surface area, surface charge density, total amount of surface charge and surface electric field intensity. This method marks a breakthrough in the field of determining surface property parameters of a substance. However, this method also has some weakness: (1) This method may need quite long time to determine surface property, due to the method is based on ion exchange equilibrium experiment, and the ion exchange equilibrium in actual system often requires considerable time. (2) Due to different materials have different surface charge amount and charge density, the time required for ion exchange equilibrium may vary significantly. Thus, in practice, it may be difficult to control the equilibrium state with this method. (3) In this method, it is required to calibrate three parameters, i.e., βA, βB and m with standard sample, in which βA, βB may be easy to be accurately calibrated, but accurate calibration of m may have difficulty. (4) This method may first need to use strong acid to treat the sample to make the tested sample to be H+ saturated, and thus may bring certain change to the substance surface property. In addition, the electrostatic bond between H+ ion and surface is far greater than that of ions such as Ca2+ and Na+, which may cause difficulty to reach exchange equilibrium.
Thus, there is a need for a system and method for determining and analyzing surface property parameters of a substance, which can overcome the shortcomings such as long equilibrium time, not easy to determine equilibrium and not easy to accurately determine m.